A typical concentrating solar energy conversion system includes a field of sun-tracking mirrors (heliostats) that focus a solar flux onto a tower mounted thermal receiver. The receiver is heated by the solar flux and transfers that heat as thermal energy to a heat transfer fluid such as water, oil, or molten salts. In other cases, solar energy is transferred to solid particles, or a gas such as carbon dioxide, which then serve the role of a heat transfer media. Some solar energy conversion plants also utilize a steam-Rankine system, which creates steam by transferring energy from a hot heat transfer fluid or media to a working fluid (e.g. water) by use of a heat exchanger. The steam is then used to drive one or more steam turbines to produce electricity. Alternatively, some solar energy conversion plants directly use a heat transfer fluid also as the working fluid to drive a turbine to produce electricity, thus eliminating the need for a heat exchanger.
Some thermal receivers are able to operate at high temperatures (e.g. 650° C. or above). However, such high temperature systems typically utilize air or solid particles as the heat transfer medium, and may suffer from low thermal efficiencies when compared to lower-temperature thermal receivers. Other receivers, such as those utilizing molten salts or steam as the heat transfer medium can achieve higher thermal efficiencies, but are unable to operate at the high temperatures found in the typical air or solid particles systems.
Of considerable interest, is supercritical carbon dioxide (s-CO2) as the working fluid in concentrating solar power systems. S—CO2 concentrating solar power systems are projected to operate with working fluid temperatures that exceed 650° C. are capable of operating as both a heat transfer fluid and a working fluid, and CO2 is a readily available, low toxicity compound. However, most concentrating solar power receivers currently available suffer from low thermal efficiencies, largely due to radiant and convective heat losses from the receivers' various hot surfaces to the environment. Thus, there remains a need in the art for higher efficiency, higher temperature thermal receivers for next-generation concentrating solar power plants.